There is an image similarity calculation method of calculating similarity between two images to be compared with each other. Generally, such image similarity calculation method is used for calculating a similarity between an inquiry image and an image for retrieval, in an image retrieval system for retrieving an image similar to the inquiry image from a group of registered images.
Patent Document 1 describes an example of the conventional image retrieval method. The image retrieval method described in Patent Document 1 divides an image into multiple blocks and calculates the feature quantity of each block. Further, the image retrieval method provides each block with a label in accordance with the feature quantity obtained for each block and generates a label matrix by arranging labels in a specified order. The image retrieval method calculates an image similarity between the inquiry image and an image for retrieval as a similarity of label columns obtained from these images. In retrieval, images for retrieval for which similarities exceed a threshold value are output as a retrieval result.
Patent Document 2 describes an image retrieval method of retrieving an image partially similar to an inquiry image. The image retrieval method described in Patent Document 2 inputs an inquiry image and an inquiry area, i.e., an area for retrieval in the inquiry image. The method divides an inquiry image into blocks. A weight is defined in accordance with an overlapping area between each block and the inquiry area. The method uses the weight to weight the feature quantity of each block to calculate the feature quantity. Similarly, the method calculates the feature quantity of an image for retrieval and compares both feature quantities to calculate the image similarity. In retrieval, images with high image similarities are output as a retrieval result.
Patent Document 3 describes an image retrieval method reflecting user's retrieval intention. The image retrieval method described in Patent Document 3 divides an inquiry image and an image for retrieval into multiple areas and allows a user to define different weights for the divided areas. The method obtains a similarity by comparing feature quantities of the corresponding divided areas between the inquiry image and the image for retrieval. The method applies the weight defined for each divided area to the similarity to calculate an image similarity. Since a user can specify an area that needs special attention during retrieval, it is possible to perform the image retrieval reflecting the user's retrieval intention.
Patent Document 1: JP-A-1999-312248 (paragraphs 0012 through 0013, FIGS. 9 and 13)
Patent Document 2: JP-A-2000-163576 (paragraphs 0017 through 0020, FIGS. 7 and 8)
Patent Document 3: JP-A-2001-134765 (paragraphs 0028 through 0031, FIG. 11)